This invention relates to speed control systems, and more particularly, to cruise control systems for controlling cruising speed of a motorized vehicle and a method therefor.
Various cruise control systems have been used with automobiles to maintain an automobile at a desired cruising speed. Typically, the driver of the automobile achieves the desired cruising speed and then activates a cruise control system which maintains the automobile at the achieved driving speed. In the past, cruise control systems have been proposed including one which used a digital-to-analog converter. However, most digital-to-analog converters fabricated with integrated circuits require a relatively large die area to make the circuit chip and also require rather accurate classical R-2R ladder networks. The present invention overcomes these and other shortcomings of using a digital-to-analog converter in a cruise control system. Also, in the past a telemetry system that employed sample and hold circuits has been modified to replace the sample and hold circuits by an analog-to-digital converter having an R-2R ladder network. However, it will be recognized that the present invention does more than employ a simple sample and hold circuit.
Accordingly, one of the objects of the present invention is to provide a cruise control integrated circuit which can be fabricated without the use of an accurate resistive network and an extremely large die area normally associated with digital-to-analog converters.
Another object of the invention is to provide a cruise control circuit that can use relatively inexpensive capacitors.
Yet another object of the present invention is to provide a cruise control system wherein the preselected speed can be gradually increased by the use of a low frequency pulse generator incrementing a latched counter.